172.16.0.X address: problem with VPN

I've heard that windows "does not like" addresses with zero, like 172.16.0.X, but did not see any oficcial document about it. However, I noticed that when my station is assigned such address, VPN based on GRE protocol does not work. When address is "normal", e.g. 172.16.45.56, etc, it works. This is GPRS connection, if it helps.

The problem with 0's, is when an IP ends in a 0 - then it is normally a network address.

For instance, 192.168.1.0/24 (mask 255.255.255.0) this address would have to be a network (or subnet) address.

However, if the network were larger (over 256 addresses) then it might encompass a "zero" within it. For instance, my own laptop right now. My network is 172.16.66.0/23 which ranges from 172.16.66.1 to 172.16.67.254. So, because I'm the network engineer and I get to pick my own IP, I took 172.16.67.0 as my IP and it works fine.

The real problem comes in with older equipment with older TCP/IP stacks which don't recognize VLSM (Variable Length Subnet Masking) - and insist that a 192.168.1.0 is a class C and can therefore only have a subnet mask of /24 and not /23 and that anything ending in .0 must be the network address.

If you have a "modern" Windows OS (like 2000, XP, 2003) this shouldn't be a problem for you.

If you are having problems with your VPN with particular addressing schemes, it may well be due to the local and remote networks having the same network ID (same subnets). Is this a possibility ? such as when both are using something like 172.168.0.x When you do so there are routing issues, the routing devices do not know to which location to send the packets and they are usually dropped.

There are a few IP addresses that are reserved for private (non-routable) networking, 192.168.0.0, 10.0.0.0, and 172.16.0.0 through 172.31.0.0. Remember that the zeros can be any number from 1 to 254. The most common private network is 192.168.0.0. The ranges are 10.1.1.1 - 10.255.255.254, 172.16.1.1 - 172.31.255.254, 192.168.1.1 - 192.168.255.254.

Private addresses are "non-routable" on the Internet - they are reserved for PRIVATE internal networks. No problems using them, until they reach a public Internet connection where they should be dropped.

As pseudocyber stated, only a '0' as the last octet is the issue and that applies to older networking equipment, though still best to avoid them if only to avoid confusion. Usually when we discus an IP ending in zeros we are not referring to an IP address but rather a subnet ID. 192.168.1.1 with a subnet mask of 255.255.255.0 would have a network ID of 192.168.1.0 or if you had a subnet mask of 255.255..0.0 it would have a network ID of 192.168.0.0

Well, it is not nailed down yet, but default gateway was not assignned sometimes. I'm creating GPRS connection, and ipconfig shows empty space in the 'Default gateway' in some cases. My IP address and DNS servers are assigned properly, but no default gateway.. Obviously, VPN connection can't work with such setup. :)

It's 4,5M cellular subscribers network. I think that Nokia GGSN is assigning addresses, and static addresses is not an option. Actually, it should be a separate paid service ("public IP address"), and we are going to provide it. I work for that cellular network actually. :)

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